Sorry that my previous thread didn't get answered but I think we can figure this out together.
I'm guessing that avoiding the use of usethis is necessary for non-package projects, but it should probably work for package projects. In either case, git2r::init() will work to initialize a git repo regardless.
renv::init() should work without much issue, I think. Something like below should get you started. Let me know if you run into any issues.
# project.dcf
Title: Project Template Name
Subtitle: Some great description...
Binding: project_fun
Parameter: git
Widget: CheckboxInput
Label: Create a git repository
Parameter: renv
Widget: CheckboxInput
Label: Initialize a project-local library
project_fun <- function(path, ...) {
dots <- list(...)
dir.create(path)
if (dots$git) git2r::init(path)
if (dots$renv) renv::init(path)
}